Method and Arrangement for Reducing Power Consumption in a Mobile Communication Network

ABSTRACT

The invention relates to a method and an arrangement for reducing power consumption of a receiver in a mobile communication network comprising a sender transmitting packet data on a downlink channel to one or more receivers over a radio interface. Inactive time instants and listening time instants are defined according to provided rules. The receiver is arranged to listen for information from the sender during the listening time instants and to sleep during the inactive time instants. Thus, less power will be consumed during the inactive time instants.

TECHNICAL FIELD

The present invention generally relates to a mobile communicationnetwork and, in particular, to an arrangement allowing for reducingpower consumption in a mobile terminal as well as a method for suchreduction. The invention further relates to a computer-readable mediumcontaining computer program for reducing power consumption in a mobileterminal.

BACKGROUND OF THE INVENTION

In packet transmission systems, the data is organized into packets andtransmitted along with control information such as the size (or startand end) of the data, and the identity of the receiver (at least whencommunicating over shared media). In many systems the time is dividedinto time frames, where each frame carries zero or more packets, alongwith the mentioned control information.

A receiver in such a system monitors the transmitted control informationfor the presence of packets that should be received by that receiver. Insituations where the bitrate required by the application is much lowerthan the transmission bitrate, the receiver is most of the timeessentially idle, just monitoring the control information.

Examples of the above include all existing cellular packet transmissiontechniques, i.e. GPRS/EDGE, WCDMA (R99, HSDPA, and E-UL), and CDMA2000(1x, Ev-DO, and Ev-DV).

With many transmission technologies, actively monitoring the controlinformation can be very power consuming, even if the control informationitself contains little information and there is no data that needs to bereceived. For example, a wideband radio transmission technique, designedfor high data bit rates, may require that the receiver demodulates andprocesses the entire frequency band even though it is only interested inthe control information. This is the case, e.g. for WCDMA HSDPA and maywell turn out to be the case for OFDM-based systems such as thelong-term evolution (LTE) of UMTS.

This means that for a low-rate service (such as voice) the powerconsumption can be significantly larger when using a wideband systemcompared to a narrowband system.

If the mobile terminal occasionally could enter a “sleep mode”, meaningthat it does not monitor the control information during a period oftime, power consumption could be reduced. This type of sleep mode iscurrently used when the mobile terminal has entered a paging state. Inpaging state the mobile terminal only occasionally listens for a “wakeup” or “paging” signal, from the network. However this method requiresadditional signaling between the network and the mobile terminal, inorder to “wake it up”, and wouldn't be appropriate to use for short timeintervals e.g. between successive packets in an ongoing real-time datasession.

SUMMARY OF THE INVENTION

Accordingly, it is an objective with the present invention to provide animproved method for reducing power consumption of a receiver in a mobilecommunication network comprising a sender transmitting packet data on adownlink channel to one or more receivers over a radio interface.

This objective has been achieved through a method according to thecharacterising portion of claim 1.

Another objective with the present invention is to provide an improvedarrangement for reducing power consumption of a receiver in a mobilecommunication network comprising a sender transmitting packet data on adownlink channel to one or more receivers over a radio interface.

This other objective has been achieved through an arrangement accordingto the characterising portion of claim 14.

A further objective with the present invention is to provide an improvedcomputer-readable medium for reducing power consumption of a receiver ina mobile communication network comprising a sender transmitting packetdata on a downlink channel to one or more receivers over a radiointerface.

This further objective is achieved through a computer-readable mediumaccording to the characterising portion of claim 28.

Further embodiments are listed in the dependent claims.

Thanks to the provision of defined sleep rules, the power consumption inmobile terminals is reduced and, thus, the battery life is increased.

The network and the terminal agree on a rule that specifies timeinstants when the network may not transmit anything to the terminal,thereby allowing the terminal to disable receiving processing. No extrasignaling is needed when the terminal should listen for controlinformation, thus enabling this technique to be used on a very shorttime interval, e.g. between successive packets in an ongoing real-timesession. Further, the proposed rule principles, as well as selectionalgorithms, are designed to work well during ongoing sessions.

When running a low-rate service over a wideband system, the sender andreceiver agrees on a sleep rule that prescribes when the sender may sendpackets to the receiver and when it may not do so. Such a rule wouldtypically specify relatively long periods when no packets should betransmitted to the receiver, allowing the receiver to stop monitoringthe media for control information.

Still other objects and features of the present invention will becomeapparent from the following detailed description considered inconjunction with the accompanying drawings. It is to be understood,however, that the drawings are designed solely for purposes ofillustration and not as a definition of the limits of the invention, forwhich reference should be made to the appended claims. It should befurther understood that the drawings are not necessarily drawn to scaleand that, unless otherwise indicated, they are merely intended toconceptually illustrate the structures and procedures described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, wherein like reference characters denote similarelements:

FIG. 1 shows an exemplary block diagram over a communication network;

FIG. 2 shows a state diagram of a user equipment having the presentinvention implemented.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 depicts a communication system, such as a WCDMA communicationsystem, including a Radio Access Network (RAN), such as the UMTSTerrestrial Radio Access Network (UTRAN) architecture, comprising atleast one Radio Base Station (RBS) (Base Station (BS) or Node B) 15connected to one or more Radio Network Controllers (RNCs) 10. The RAN isconnected to a Core network (CN) 12. The RAN and the CN 12 providecommunication and control for a plurality of user equipments (UE) 18(only one is shown in FIG. 1), that each uses downlink (DL) channels 13(i.e. base-to-user or forward) and uplink (UL) channels 14 (i.e.user-to-base or reverse). On the downlink channel 13, the RBS 15transmits to each user equipment 18 at respective power level. On theuplink channel 14, the user equipments 18 transmit data to the RBS 15 atrespective power level. According to a preferred embodiment of thepresent invention, the communication system is herein described as aWCDMA communication system. The skilled person, however, realizes thatthe inventive method and arrangement works very well on any packet basedsystem.

A sleep rule should be setup between a pair of sender and receiver. Inthe sender, the rule specifies when the sender is allowed to transmitpackets to the receiver. These time instants will be referred to as theactive awake periods, while the remaining time instants will be calledactive sleep periods (inactive periods). During active sleep periods,the receiver can turn off its reception, demodulation, and processinghardware and software, thereby saving power.

The active sleep mode according to the invention is different from theinactive sleep mode according to prior art. In the prior art inactivesleep mode, the terminal is only listening on a paging channel and istypically assigned a long Radio Network Temporary Identifier (RNTI). Theterminal needs a wake-up message on the paging channel to be able toreceive any information. In order to achieve an effective scheduling,the terminal needs a shorter RNTI, which requires additional signaling.

In the active sleep mode according to the present invention, theterminal typically has a short RNTI, but it is not possible to addressthe terminal unless it is in an active awake mode. However, thetransition from the active sleep state to the active awake staterequires no signaling at all.

If the active awake periods of two or more terminals are configured suchthat they do not overlap in time then it is possible to use the sameshort RNTI for all these terminals. The base station may then use theshared short RNTI in the transmission time interval corresponding toactive awake period of the terminal it needs to address. This can beused to increase the efficiency of the control signaling since there isonly a limited number of unique RNTI sequences of any given length, andin order for the control signaling to consume little resources the shortRNTIs shall be of as short length as possible.

FIG. 2 shows a state diagram, in which an active state of the UE isdenoted with 20. When the UE is active, it is assigned a short RadioNetwork Temporary Identifier (RNTI) and may send and receive data.According to the present invention, the active state 20 has been dividedinto an active awake state 21 and an active sleep state 22.

In the active awake state 21:

-   -   both UE and BS initiated actions are allowed;    -   the UE may receive DL control information, demodulate and decode        the control channel;    -   the UE may receive DL data.

In the active sleep state 22:

-   -   only UE initiated actions are performed:    -   UL transmissions possible:    -   Measurements, channel estimation, cell search etc are possible;    -   Demodulation and decoding of the control channel may be turned        off.

The transition 24 from the active sleep state 22 to the active awakestate 21:

-   -   is triggered by pre-determined rules (pattern);    -   is immediate with no additional signaling required;    -   can not be initiated from the transmitter.

The transition 24 from the active awake state 21 to the active sleepstate 22:

-   -   may be triggered by pre-determined rules (pattern);    -   may also be initiated from the transmitter, e.g. with a specific        command or as a result of transmitting a packet to the receiver;    -   is immediate with no additional signaling required.

On the contrary to the active state 20, the UE also have an inactivesleeping state denoted with 23. In the inactive sleeping state 23:

-   -   the receiver radio of the UE is periodically turned off;    -   the UE only listens to paging messages from the BS;    -   the UE is assigned a long RNTI;    -   the transmitter radio of the UE may also be turned off.

The transition 25 between the active state 20 and the inactive sleepstate 23:

-   -   the BS may only trigger transitions from inactive sleeping 23 to        active 20 state by transmitting explicit wake-up signaling.    -   When entering the active state 20, the UE will also enter one of        the sub-states active awake 21 or active sleep 22 by following a        pre-defined rule;    -   A timer or explicit signaling may trigger transitions from the        active 20 to the inactive sleeping state 23.

There are two steps of the invention: principles for sleep rules, andalgorithms to select sleep rules suitable in specific scenarios.

In the following when discussing the “active” mode/period it is theactive awake state mode/period that is meant and when discussion the“sleep” mode/period it is the active sleep mode/period that is meant.

One straightforward principle is to specify a fixed pattern of activeperiods and sleep periods. Such a pattern would typically be periodic.For example, in the case of voice (telephony) applications, it couldamount to a short active period (a few frames) every 20 ms.

A drawback of a fixed pattern is the inherent conflict between schedulerflexibility and power consumption. If the active period is very short,the sender has little or no freedom as to which receiver to transmit toat what time, which can reduce the transmission efficiency. A longeractive period gives the scheduler more freedom but requires the receiverto listen actively for a longer period, reducing the power consumptiongain.

A slightly more advanced rules principle is to specify that each activeperiod starts at a predetermined time and ends when a packet has beenreceived, after which the receiver can go back to sleep mode. Suchdynamic active periods may be specified to start periodically, e.g. onceevery 20 ms. If no packet is transmitted during an active period, itextends until the next active period would anyway have started.Alternatively, the active period may be specified to end after a certaintime, e.g. 5 ms, if no packet is transmitted.

To shorten the active period for the receiver when there is nothing toreceive, the sender may send dummy/empty packets to the receiver inorder to force the receiver to go into sleep mode. This can beadvantageous especially in low and medium load situations when there isunused transmission capacity available.

More generally, sleep commands may be embedded in the transmission. Forinstance, the network may send a few packets followed by a command thatinstructs the terminal to sleep for a certain time interval, or until acertain time when it should wake up.

The sleep rules may also be connected with retransmissions. If a packethas been received in error, and the receiver informs the sender by meansof a negative acknowledgement, a new active period can be defined tostart as a result. The extent of this active period should be coupled tothe nature of retransmissions. For example, it should not start earlierthan the earliest time at which a retransmission can possibly occur,e.g. due to delays in transmission and processing of theacknowledgement. Further, if the retransmission scheme mandates thatretransmissions shall occur at a certain exact time instant, the activeperiod should be set to only include that time instant.

Another option is to relate the active periods to channel qualityreporting from the receiver. Such reporting is present for example inWCDMA HSDPA, in the form of CQI reports that are transmitted with aperiod that is signaled from the network to the terminal. It may bedesirable to keep the period long to limit the amount of radio resourcesspent on the reporting. A drawback of this is that the network hasup-to-date information about the channel quality only directly after aCQI report. The accuracy of that information then reduces as timepasses, until the next report. In such cases, it may be advantageous tospecify the sleep rule such that each active period begins slightlyafter a CQI report, so that the network can utilize up-to-dateinformation about the channel quality.

Naturally, sleep rules should be selected dependent on the type oftraffic in order to be efficient. This could either be done based onknowledge of the application type (e.g. if it is a speech call or avideo call), agreed QoS for the traffic, or based on the observed natureof the traffic.

If explicit information about particular applications is available, e.g.from higher layers, then pre-designed sleep rules can be tabulated forsome applications. For instance, a speech application may have a sleeprule where the terminal enters sleep mode immediately upon reception ofa data packet, and periodically returns to active mode every 20 ms, asdiscussed above.

More generally, the desired nature of the radio connection may be knownin a parameterized form, e.g. in the form of RAB parameters [ref to 3GPPspec] or other type of QoS agreement. This may for instance include themaximum bit rate, guaranteed bit rate, maximum packet size, and maximumdelay. Then the sleep rule can be selected automatically by means of analgorithm. For example, the sleep rule may be designed to enter theactive period periodically with a period that is determined from the QoSparameters. The period may be calculated by comparing the maximumincoming traffic bit rate with the estimated bit rate over the radio,such that it is likely that, at each active period, all buffered datacan be transmitted in a single transmission. With such an algorithm, thesleep rule may be dynamically updated based on changes in the estimatedbit rates.

An alternative may also be to use an adaptive algorithm that determinesthe sleep rules based on observed traffic characteristics. An examplecan be to monitor the inter-arrival time between packets for each userand dynamically adapt the sleep rule to this time. This can be doneeither in the network or in the terminal (or even both), depending onthe nature of the control signaling defined to setup the sleep rules.

The invention, if properly implemented, can significantly reduce thepower consumption in the terminal, thereby increasing the battery life.

It will be appreciated that at least some of the procedures describedabove are carried out repetitively as necessary to respond to thetime-varying characteristics of the channel between the transmitter andthe receiver. To facilitate understanding, many aspects of the inventionare described in terms of sequences of actions to be performed by, forexample, elements of a programmable computer system. It will berecognized that the various actions could be performed by specializedcircuits (e.g. discrete logic gates interconnected to perform aspecialized function or application-specific integrated circuits), byprogram instructions executed by one or more processors, or acombination of both.

Moreover, the invention can additionally be considered to be embodiedentirely within any form of computer-readable storage medium havingstored therein an appropriate set of instructions for use by or inconnection with an instruction-execution system, apparatus or device,such as computer-based system, processor-containing system, or othersystem that can fetch instructions from a medium and execute theinstructions. As used here, a “computer-readable medium” can be anymeans that can contain, store, communicate, propagate, or transport theprogram for use by or in connection with the instruction-executionsystem, apparatus or device. The computer-readable medium can be, forexample but not limited to, an electronic, magnetic, optical,electromagnetic, infrared, or semiconductor system, apparatus, device orpropagation medium. More specific examples (a non-exhaustive list) ofthe computer-readable medium include an electrical connection having oneor more wires, a portable computer diskette, a random access memory(RAM), a read only memory (ROM), an erasable programmable read onlymemory (EPROM or Flash memory), an optical fibre, and a portable compactdisc read only memory (CD-ROM).

Thus, a computer-readable medium containing computer program accordingto a preferred embodiment of the present invention for reducing powerconsumption of a mobile terminal in a communication network comprising asender transmitting packet data on a downlink channel to one or morereceivers over a radio interface, wherein the computer program performsthe step of: defining inactive time instants and listening timeinstants, during which said receiver is listening for signalling fromsaid sender, whereby less power is consumed during said inactive timeinstants.

Modifications to embodiments of the invention described in the foregoingare possible without departing from the scope of the invention asdefined by the accompanying claims. Expressions such as “including”,“comprising”, “incorporating”, “consisting of”, “have”, “is” used todescribe and claim the present invention are intended to be constructedin a non-exclusive manner, namely allowing for items, components orelements not explicitly described also to be present. Reference to thesingular is also to be construed to relate to the plural and vice versa.

Numerals included within parentheses in the accompanying claims areintended to assist understanding of the claims and should not beconstrued in any way to limit subject matter claimed by these claims.

1. A method for reducing power consumption of a receiver in a mobilecommunication network comprising a sender transmitting packet data on adownlink channel to one or more receivers over a radio interface,characterised in that the method comprises the step of: defininginactive time instants and listening time instants, during which saidreceiver is listening for signalling from said sender, whereby lesspower is consumed during said inactive time instants.
 2. A methodaccording to claim 1, characterised in that the method further comprisesthe step of defining said listening time instants according to a fixedperiodical pattern.
 3. A method according to claim 1, characterised inthat said listening time instants starts at a pre-determined time andends when a packet is received in said receiver.
 4. A method accordingto claim 3, characterised in that the method further comprises the stepof sending a dummy packet to said receiver in order to end saidlistening time instants.
 5. A method according to claim 1, characterisedin that said listening time instants starts at a pre-determined time andends after a pre-determined time.
 6. A method according to claim 1,characterised in that the method further comprises the step of sendingcommands instructing said receiver to go into said inactive mode for atime period according to instructions in said command.
 7. A methodaccording to claim 1, characterised in that the method further comprisesthe step of sending commands instructing said receiver to go into saidinactive mode until a pre-determined time.
 8. A method according toclaim 1, characterised in that the method further comprises the step oftriggering the start of said listening time instant by a negativeacknowledgement sent from said receiver when a packet is erroneouslyreceived in said receiver.
 9. A method according to claim 1,characterised in that said listening time instant starts after a channelquality report is received in said receiver.
 10. A method according toclaim 1, characterised in that the method further comprises the step ofproviding rules according to which said time instants are defined.
 11. Amethod according to claim 10, characterised in that said rules aretabulated for different types of applications.
 12. A method according toclaim 10, characterised in that the method further comprises the step ofautomatically selecting said rules by means of an algorithm based onpre-determined parameters.
 13. A method according to claim 10,characterised in that the method further comprises the step ofdetermining said rules by means of an adaptive algorithm based onobserved traffic characteristics.
 14. An arrangement for reducing powerconsumption of a receiver in a mobile communication network comprising asender transmitting packet data on a downlink channel to one or morereceivers over a radio interface, characterised in that the arrangementcomprises: means for defining inactive time instants and listening timeinstants, during which said receiver is arranged to listen forsignalling from said sender, whereby less power is consumed during saidinactive time instants.
 15. An arrangement according to claim 14,characterised in that the arrangement further comprises means fordefining said listening time instants according to a fixed periodicalpattern.
 16. An arrangement according to claim 14, characterised in thatsaid listening time instants are arranged to start at a pre-determinedtime and to end when a packet is received in said receiver.
 17. Anarrangement according to claim 16, characterised in that the arrangementfurther comprises means for sending a dummy packet to said receiver inorder to end said listening time instants.
 18. An arrangement accordingto claim 14, characterised in that said listening time instants arearranged to start at a pre-determined time and to end after apre-determined time.
 19. An arrangement according to claim 14,characterised in that the arrangement further comprises means forsending commands instructing said receiver to go into said inactive modefor a time period according to instructions in said command.
 20. Anarrangement according to claim 14, characterised in that the arrangementfurther comprises means for sending commands instructing said receiverto go into said inactive mode until a pre-determined time.
 21. Anarrangement according to claim 14, characterised in that the arrangementfurther comprises means for triggering the start of said listening timeinstant by a negative acknowledgement sent from said receiver when apacket is erroneously received in said receiver.
 22. An arrangementaccording to claim 14, characterised in that said listening timeinstants are arranged to start after a channel quality report isreceived in said receiver.
 23. An arrangement according to claim 14,characterised in that said means for defining time instants is arrangedto define said time instants according to provided rules.
 24. Anarrangement according to claim 23, characterised in that said rules aretabulated for different types of applications.
 25. An arrangementaccording to claim 23, characterised in that the arrangement furthercomprises means for automatically selecting said rules by means of analgorithm based on pre-determined parameters.
 26. An arrangementaccording to claim 23, characterised in that the arrangement furthercomprises means for determining said rules by means of an adaptivealgorithm based on observed traffic characteristics.
 27. A mobileterminal, characterised in that it comprises an arrangement according toany of claims 14-26.
 28. A computer-readable medium containing computerprogram for reducing power consumption of a receiver in a mobilecommunication network comprising a sender transmitting packet data on adownlink channel to one or more receivers over a radio interface,characterised in that the computer program performs the step of:defining inactive time instants and listening time instants, duringwhich said receiver is listening for signalling from said sender,whereby less power is consumed during said inactive time instants.